Old, "multiyear" ice -- the glue that holds the polar ice cap together and forms the Arctic's defense against encroaching warming -- is slowly disintegrating, a process that is plain to see from the air.

Thick ice floes used to be kilometers (miles) wide just over a decade ago, said Jim Overland, a sea-ice expert with the U.S. National Oceanic and Atmospheric Administration, who has been surveying the site since the 1990s.

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Now the narrow floes -- with bright-white tops and a blue underwater glow -- are just meters (yards) wide, observed Overland as he studied the patterns from the window of a U.S. Coast Guard C-130 aircraft.

The dense, high-quality ice is not coming back, Overland said.

"That's a one-way street," he said "We have the same amount of multiyear ice this year as last year, even though we have a little more ice overall."